Vapor compression cycles are used in refrigeration, space cooling and space heating applications. Typical vapor compression cycles involve compressing and decompressing a refrigerant in a closed loop system and circulating the refrigerant through an evaporator and a condenser. The refrigerant serves to absorb thermal energy in the form of heat from the evaporator and transport the thermal energy to the condenser where it can be released. In refrigeration and cooling applications heat is absorbed from a space by the refrigerant during an evaporation portion of the cycle where the refrigerant changes into a vapor phase. The absorption of heat provides useful cooling of the space. The vapor is subsequently compressed in a compressor. Energy is consumed by the compressor during the compression of the vapor. Compression of the vapor facilitates condensation of the vapor into a liquid. Condensation of the vapor is caused by flowing the compressed vapor through a condenser where heat is released into a heat sink thereby condensing the refrigerant into a liquid. The liquid is circulated through the closed loop to a decompression device, typically an expansion valve, where the pressure of the refrigerant is decreased. Typically, the refrigerant pressure is reduced by a factor of five or more. The decompressed refrigerant is returned to the evaporator resuming the cycle. Although decompression of the refrigerant is desirable to bring the pressure of the refrigerant to within a desired operating range prior to entering the evaporator, kinetic energy losses are experienced across the expansion valve. This kinetic energy loss is typically not recovered and therefore energy input is required for compressing the vapor in the compressor.
In an effort to improve the efficiency of vapor compression cycles, it is desirable to recover the kinetic energy lost during decompression of the refrigerant across the expansion valve. Venturi nozzles have been used to help recover some of the kinetic energy associated with decompression of the refrigerant. Typically, venturi nozzles are comprised of a fluid conduit having an inlet, an outlet and throat disposed therebetween. The flow area of the throat is less than that of the inlet and the outlet. The velocity of the fluid flowing in the throat is greater than the velocity of the fluid flowing at the inlet and the outlet. As a result of conservation of momentum the pressure at the throat is less than the pressure at the inlet and the outlet. A fluid port is generally connected to the throat to entrain fluid therethrough. The pressure at the outlet of venturi nozzles is an intermediate pressure between the pressure at the venturi inlet and the pressure at the fluid port connected to the throat.
Efficiency of a refrigeration system can be increased with the use of a venturi. The fluid port at the throat of the venturi is connected to an outlet of the evaporator and the venturi inlet is connected to an outlet of the condenser. A liquid-vapor mixture of refrigerant is thus produced at the outlet of the venturi at an intermediate pressure between the pressure at the venturi inlet and that at the throat of the venturi. After the liquid-vapor mixture exits the venturi, liquid and vapor phases are separated. The liquid refrigerant is decompressed through an expansion valve which discharges into the evaporator; and vapor is supplied to the compressor suction at the intermediate pressure. Therefore, the compressor requires less energy input to achieve a desired compression and the refrigeration system efficiency is increased. However, because the venturi recovers only a portion of the kinetic energy and losses through the expansion valve are not recovered, further system efficiency improvements are needed.
Referring to FIG. 1, during operation of a prior art refrigeration cycle 60, the refrigerant absorbs energy from an evaporator which increases the enthalpy of the refrigerant between points 61 and 62. A compressor provides the entire pressurization from between points 62 and 63. A condenser provides a heat sink for removing energy from the refrigerant thereby reducing the enthalpy of the liquid refrigerant between points 63 and 66, at a substantially constant pressure. Liquid refrigerant exiting the condenser is decompressed by throttling through a decompression device thereby reducing the pressure of the refrigerant between points 66 and 61.
There is a need to provide a refrigeration cycle with a more efficient refrigerant pressurization system. Prior art methods and systems for addressing these needs were too inefficient or ineffective or a combination of these. Based on the foregoing, it is the general object of the present invention to improve upon or overcome the problems and drawbacks of the prior art.